Late pleistocene and halocene sea-level changes in Japan: implications for tectonic histories and mantle rheology

It is very important to separate the tectonic and glacial-isostatic components in the observed Holocene and Late Pleistocene sea-level changes in tectonically active areas such as Japan for studying tectonic processes and for constraining mantle rheology. The separation can be achieved by considering the spatial dependence of the relative sea-level on the geometry of the coastline around the site where sea-level is evaluated. In fact, the relative sea-level caused by the last deglaciation at sites in the embayment such as Tokyo and Osaka has a sea-level curve with a high stand at mid-Holocene, and that site situated on the tip of peninsula has a sea-level curve culminating towards the present. The geometric effect also causes the regional difference of the sea-level variations in the late glacial phase. In the Japanese Islands, the regional difference of the predicted relative sea-level is about 5 m at 6000 years ago, 20 m at 10,000 years ago and 30 m at 18,000 years ago. Comparison between observations and predictions indicates that the observations at several sites in Japan are consistent with the predicted sea-level variations. More systematic data is required for the period 18,000 years ago to the present in order to examine tectonic processes and mantle rheology.